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https://issues.apache.org/jira/browse/HDFS-4799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13652181#comment-13652181
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Todd Lipcon commented on HDFS-4799:
-----------------------------------
Thanks for the review, Aaron. I'm going to leave this open for another day
before committing, just because it's an important bug and a subtle area of the
code. If some of the other folks watching this ticket want to take a look,
would be very much appreciated.
> Corrupt replica can be prematurely removed from corruptReplicas map
> -------------------------------------------------------------------
>
> Key: HDFS-4799
> URL: https://issues.apache.org/jira/browse/HDFS-4799
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.0.4-alpha
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Blocker
> Attachments: hdfs-4799.txt, hdfs-4799-unittest.txt
>
>
> We saw the following sequence of events in a cluster result in losing the
> most recent genstamp of a block:
> - client is writing to a pipeline of 3
> - the pipeline had nodes fail over some period of time, such that it left 3
> old-genstamp replicas on the original three nodes, having recruited 3 new
> replicas with a later genstamp.
> -- so, we have 6 total replicas in the cluster, three with old genstamps on
> downed nodes, and 3 with the latest genstamp
> - cluster reboots, and the nodes with old genstamps blockReport first. The
> replicas are correctly added to the corrupt replicas map since they have a
> too-old genstamp
> - the nodes with the new genstamp block report. When the latest one block
> reports, chooseExcessReplicates is called and incorrectly decides to remove
> the three good replicas, leaving only the old-genstamp replicas.
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